Low temperature liquid storage tank having crack-detecting means

ABSTRACT

The low temperature liquid storage tank having crack-detecting means of the present invention is provided with at least a heat insulating layer and at least an impermeable layer applied to the inner wall of the tank shell in laminated relationship with each other. A plurality of hermetically sealed sources of radioisotope are secured to the inner surface of the tank shell so that any crack in the impermeable layer, if such is generated, can be detected by detecting leakage of radiation from the sources through such a crack by a dosimeter.

United States Patent Katsuta Oct. 28, 1975 LOW TEMPERATURE LIQUIDSTORAGE 2,674,695 4/1954 Grace 250/357 TANK HAVING CRACK DETECTING2,794,953 6/1957 Callender... 250/303 MEANS 3,439,166 4/1969 Chope250/358 3,531,638 9/1970 Badgett 250/364 [75] Inventor: Kihei Katsuta,Nagasaki, Japan [73] Assignee: Mitsubishi Jukogyo Kabushiki PrimaryExaminer-mold Dixon Kaisha, Tokyo Japan Attorney, Agent, or FzrmCushman,Darby &

Cushman [22] Filed: June 13, 1974 [21] Appl. No.: 479,143 [57] ABSTRACTThe low temperature liquid storage tank having crack- [30] F iApplication priority m detecting means of the present invention isprovided J 22, 1973 J n 2 with at least a heat insulating layer and atleast an imune apan 48 7055 permeable layer applied to the inner wall ofthe tank [52] Us. CL 250/303 250/364 shell in laminated relationshipwith each other. A plu- [511 Int. GOIT U161 rality of hermeticallysealed sources of radio-isotope [58] Field of l 312 358 are secured tothe inner surface of the tank shell so 250/357 that any crack in theimpermeable layer, if such is generated, can be detected by detectingleakage of ra- [56] References Cited diation from the sources throughsuch a crack by a do- UNITED STATES PATENTS 2,518,327 8/1950 Jahn 250303 11 Claims, 4 Drawing Figures U.S. Patent Oct. 28, 1975 Sheet 1 of23,916,189

LOW TEMPERATURE LIQUID STORAGE TANK HAVING CRACK-DETECTING MEANSBACKGROUND OF THE INVENTION The present invention relates to a lowtemperature liquid storage tank having crack-detecting means and,

more particularly, to a low temperature liquid storage of the internalheat insulating type having crack-detecting means wherein at least aheat insulating layer and at least an impermeable layer are laminated onthe inner wall of the tank shell.

Heretofore, in a low temperature liquid storage tank of the internalheat insulating type, it has been extremely difficult to discover cracksgenerated in the impermeable layer provided on the inner wall of thetank shell. In case an impermeable layer of a thin metallic sheet isprovided at the innermost side of the internal heat insulating layer, aclearance is formed between the impermeable layer and the heatinsulating layer into which clearance a gas such as ammonia gas isintroduced, and detecting liquid is applied along the seam of themetallic thin sheet of the impermeable layer so that any crack in theseam, if such is generated, can be detected by the detecting liquid.

However, the use of a thin metallic sheet as the impermeable layer iseconomically disadvantageous, and, in case a clearance is formed betweenthe thin metallic sheet and the heat insulating layer, the thin metalliclayer might be subjected to breakage by the movement of the lowtemperature liquid in the tank caused by the rolling of the ship. Toavoid such a defect, it has been proposed to provide in place of themetallic thin sheet an impermeable layer comprised of a synthetic resinlayer and a metallic foil applied closely in contact with the surface ofthe heat insulating layer or to provide a secondary impermeable layer inthe interior of the heat insulating layer. However, problems arise insuch an impermeable layer that detection of cracks (including pinholes)is extremely difficult.

SUMMARY OF THE INVENTION The present invention aims at avoiding thedifficulties in the prior art low temperature liquid storage tank.

Therefore, the object of the present invention is to provide a novel anduseful low temperature liquid storage tank having crack-detecting meansin which detection of cracks possibly generated in the impermeable layerof the tank can be easily and exactly effected by the provision ofsources of radioactive element on the inner wall of the tank shell.

The low temperature liquid storage tank having crack-detecting means inaccordance with the present invention comprises at least a heatinsulating layer and at least an impermeable layer applied to the innerwall of the tank shell in laminated relationship with each other, thetank being characterized in that a plurality of hermetically sealedsources of radioisotope are secured to the inner surface of the tankshell in spaced relationship from each other.

By the low temperature liquid storage tank having crack-detecting meansof the present invention described above, since a plurality ofhermetically sealed sources of radioisotope are provided in thedistributed condition along the inner surface of the tank shell, anycrack which might be generated in the impermeable .ried out therebygreatly improving the security of the tank.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic cross-sectionalview showing the hull of a ship in which a low temperature liquefied gasstorage tank having crack-detecting means in accordance with the presentinvention is incorporated;

FIG. 2 is a fragmentary cross-sectional view in enlarged scale showingin detail a portion of the low temperature liquefied gas storage tank ofFIG. 1;

FIG. 3 is a diagram showing the results of measurement of the emissivityof radiation given in relation to the conditions shown in FIG. 2; and

FIG. 4 is a fragmentary cross-sectional view showing in more detail theconstruction of the source of radioisotope shown in circle A in FIG. 2.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT Referring to FIG. I, aprimary impermeable layer 3 made of a low temperature resistant materialis provided on the inside of the tank shell 1 forming the hull with theinterposition of a heat insulating layer 2 of a material such as foamedresin. Ballast tanks B are provided at both the ships sides and theships bottom. The space L is used to receive the low temperature liquidfor storage thereof.

In FIG. 2, a secondary impermeable layer 4 is shown as being provided inthe interior of the heat insulating layer Z'arranged between the tankshell 1 and theinnermost primary impermeable layer 3.

In accordance with the characteristic feature of the present invention,a plurality of hermetically sealed sources 5 of radioisotope (only oneof which is shown in FIG. 2) are secured to the inner surface of thetank shell 1 in spaced relationship from each other.

The heat insulating layer 2 is divided into a primary heat insulatinglayer 2a and a secondary heat insulating layer 2b by the secondaryimpermeable layer 4. As to the material for forming these heatinsulating layers 2a, 2b, a material having a superior heat insulatingproperty such as hard polyurethane foam, polystyrene foam andpolyethylene foam may be employed.

As to the material for forming the tank shell 1, an ordinary steel forship construction may be used which is not noted for having a lowtemperature resistant property. However, as to the material for formingthe primary impermeable layer 3 and the secondary impermeable layer 4, acomposite low temperature resistant material such as a material sold bythe Tradename Aluminilar having metallic foils of a high malleabilityand a low gas permeability such as aluminum foils laminated withpolyester resin and a composite material having glass fibers or carbonfibers combined with polyurethane resin, epoxy resin, silicone resin ofpolytetrafluoroethylene, tetrafloroethylene copolymer must be used.

Referring to FIG. 4, the hermetically sealed source-5 of radioisotope issecured to the inner surface of the tank shell I by means of bondingagent 6 and received in the recess of the second heat insulating layer2b. The

sealed container a made of lead of the source 5 is formed with a window5b opening toward the interior of the tank. A capsule 5c is housed inthe container 5a and a predetermined quantity of radioisotope 5d (cobalt60, for example) is hermetically housed in the capsule 5c.

Thus, when the emissivity of radiation from the source 5 is measuredfrom within the tank at the periodical inspection by a suitableinstrument such as a dosimeter, results shown in FIG. 3 are obtained, ifcracks CI, CII exist in the primary and secondary impermeable layers 3,4 as shown in FIG. 2. By the inspection of the values of the peaks a, bin FIG. 3, it can be determined in which of the primary impermeablelayer 3 and the secondary impermeable layer 4 the crack is generated,and then, by investigating the positions A, B on the primary impermeablelayer 3, the positions of cracks Cl, CII can be easily determinedgeometrically.

The inspection of cracks as described above can be effected during theconstruction of the tank. The crack inspection is to be carried out atthe time the secondary impermeable layer 4 has been completed and at thetime the primary impermeable layer 3 has been completed.

As to the radioisotope to be sealed in the source S, cobalt 60 can beused most easily. In other words, the half life of cobalt 60 is 5.2years, and, assuming that the depreciation period of the ship having thelow temperature liquid storage tank described above is years, thequantity of the radioisotope as the source 5 merely decreases to aboutone-sixteenth, and the quantity of lane of radioisotope suffices for onesource. Thus, the total quantity of the sources in a ship may be in theorder of 1 mac thereby permitting the total quantity of the sources tobe limited to the degree capable of sufficiently insuring the securityof the ship.

I claim:

1. Apparatus, comprising:

wall means defining a liquid storage tank;

at least one layer of heat insulating material laminated to and coveringsaid wall means inside the tank;

at least one layer of low temperature liquid-impermeable materiallaminated to and covering said one layer of heat insulating materialinside the tank;

whereby the tank is adapted for storing low temperature liquid;

a plurality of hermetically sealed sources of radioisotope secured onsaid wall means in spaced relationship to one another, each sourceincluding shielding providing window means oriented toward the inside ofthe tank, so that cracks in the at least one 4 low temperatureliquidimpermeable layer may be detected from within the tank.

2. The apparatus of claim 1, wherein:

the hermetically sealed sources of radioisotope are each constituted bya capsule of cobalt 6O encased in lead.

3. The apparatus of claim 1, comprising:

a second layer of heat insulating material laminated to and covering thefirst-described layer of layer of low temperature liquid-impermeablematerial inside the tank; and

a second layer of low temperature liquid-impermeable material laminatedto and covering the second layer of heat insulating material inside thetank, whereby,

the second layer of low temperature liquid-impermeable materialfunctions as the primary layer of low temperature liquid-impermeablematerial and the first-described layer of low temperatureliquidimpermeable material functions as a secondary layer of lowtemperature liquid-impermeable material.

4. The apparatus of claim 1, wherein:

further including a tanker ship for transporting liquefied gas, saidship incorporating said liquid storage tank.

5. The apparatus of claim 1, wherein:

said wall means is constituted by steel.

6. The apparatus of claim 1, wherein:

the heat insulating material is constituted by rigid foamed plasticresin.

7. The apparatus of claim 6, wherein:

the at least one layer of low temperature liquidimpermeable material isconstituted by a composite aluminum foil laminated with polyester resin.

8. The apparatus of claim 6, wherein:

the at least one layer of low temperature liquidimpermeable material isconstituted by a composite of fiber reinforced polyurethane resin.

9. The apparatus of claim 6, wherein:

the at least one layer of low temperature liquidimpermeable material isconstituted by a composite of fiber-reinforced epoxy resin.

10. The apparatus of claim 6, wherein:

the at least one layer of low temperature liquidimpermeable material isconstituted by a composite of fiber-reinforced silicone resin.

11. The apparatus of claim 6, wherein:

the at least one layer of low temperature liquidimpermeable material isconstituted by a composite of fiber-reinforcedpolytetrafluoroethylene-tetrafluoroethylene copolymer.

1. Apparatus, comprising: wall means defining a liquid storage tank; atleast one layer of heat insulating material laminated to and coveringsaid wall means inside the tank; at least one layer of low temperatureliquid-impermeable material laminated to and covering said one layer ofheat insulating material inside the tank; whereby the tank is adaptedfor storing low temperature liquid; a plurality of hermetically sealedsources of radioisotope secured on said wall means in spacedrelationship to one another, each source including shielding providingwindow means oriented toward the inside of the tank, so that cracks inthe at least one low temperature liquidimpermeable layer may be detectedfrom within the tank.
 2. The apparatus of claim 1, wherein: thehermetically sealed sources of radioisotope are each constituted by acapsule of cobalt 60 encased in lead.
 3. The apparatus of claim 1,comprising: a second layer of heat insulating material laminated to andcovering the first-described layer of layer of low temperatureliquid-impermeable material inside the tank; and a second layer of lowtemperature liquid-impermeable material laminated to and covering thesecond layer of heat insulating material inside the tank, whereby, thesecond layer of low temperature liquid-impermeable material functions asthe primary layer of low temperature liquid-impermeable material and thefirst-described layer of low temperature liquid-impermeable materialfunctions as a secondary layer of low temperature liquid-impermeablematerial.
 4. The apparatus of claim 1, wherein: further including atanker ship for transporting liquefied gas, said ship incorporating saidliquid storage tank.
 5. The apparatus of claim 1, wherein: said wallmeans is constituted by steel.
 6. The apparatus of claim 1, wherein: theheat insulating material is constituted by rigid foamed plastic resin.7. The apparatus of claim 6, wherein: the at least one layer of lowtemperature liquid-impermeable material is constituted by a compositealuminum foil laminated with polyester resin.
 8. The apparatus of claim6, wherein: the at least one layer of low temperature liquid-impermeablematerial is constituted by a composite of fiber reinforced polyurethaneresin.
 9. The apparatus of claim 6, wherein: the at least one layer oflow temperature liquid-impermeable material is constituted by acomposite of fiber-reinforced epoxy resin.
 10. The apparatus of claim 6,wherein: the at least one layer of low temperature liquid-impermeablematerial is constituted by a composite of fiber-reinforced siliconeresin.
 11. The apparatus of claim 6, wherein: the at least one layer oflow temperature liquid-impermeable material is constituted by acomposite of fiber-reinforcedpolytetrafluoroethylene-tetrafluoroethylene copolymer.